The present invention relates to a process for recovering heat in an isotopic exchange installation between a liquid and a gas and an installation performing said process. In more particularly applies to an installation for the extraction of tritium from heavy water D.sub.2 O or light water H.sub.2 O used as a moderator of a nuclear reactor or as a reprocessing plant effluent, using a gas such as deuterium or hydrogen. It can also apply to the extraction or separation of an isotope from hydrogen.
Tritium is radio active and must be extracted from the light or heavy water in which it is produced by a nuclear reaction between neutrons and atoms of deuterium, deuterium being itself an isotope of the hydrogen atom.
It is possible to extract the titrium from the water to be treated in accordance with a process of the type described in French pat. No. 1 526 867, filed on Aug. 9, 1966 in the name of the C.E.A. According to the known process (cf FIG. 1a), there is a a continuous branching off of a fraction of the water contained in a nuclear reactor or the like 1. This fraction 3 is subject to an isotopic exchange reaction with a gas 5, such as deutrium or hydrogen in order to lower the titrium content of the water. This exchange takes place in an isotopic exchange reactor 7, the complete isotopic exchange installation comprising one or more such reactors arranged in series, as is shown in FIG. 1a, where there are three stages a, b, c.
In order for the isotopic exchange reaction to take place, the water must be vaporized before entering each reactor 7 by a vaporizer 11. A cooler 13 at the outlet of each reactor 7 separates the two phases and condenses the vapor and cools the gas. The gas is in co-current with the water to be treated in each reactor 7, but in counter-current in the overall installation. The tritium-enriched gas is then recycled in a distillation installation 9, before being passed to isotopic exchange reactor 7.
FIG. 1b shows the MacCabe and Thiele diagram corresponding to the installation of FIG. 1a with the tritium content of the gas on the ordinate and of the liquid on the abscissa. The water initially having a tritium content x.sub.o reacts in a first reactor with the gas having a content y.sub.2, so as to give post-exchange balanced phases of contents x.sub.1 and y.sub.1 respectively. The water with a tritium content x.sub.1 at the outlet from the first reactor 7 is contacted in the second reactor 7 with the gas having a content 7.sub.3 in order to give balanced phases with contents x.sub.2 and y.sub.2 respectively. The repetition of these operations in the other reactor or reactors 7 makes it possible to lower the tritium content of the water to the desired value.
In this type of isotopic exchange installation the number of stages, e.g. three stages, and the flow rates are generally such that heat economy problems do not arise. However, when there are numerous stages and high flow rates, the energy costs of the installation are high and heat recovery problems occur.